| Summary: | 碩士 === 國立交通大學 === 機械工程系所 === 95 === A steady two-dimensional numerical simulation is conducted to investigate the momentum, heat and mass transfer in a vertical open cavity resulting from a laminar cold air curtain flowing over the open surface of the cavity, simulating that in a vertical refrigerated display cabinet. The commercial computational fluid dynamics software PHOENICS is adopted to solve the problem. Particular attention is focused on how the parameters associated with the air curtain affect the characteristics of the flow in the cabinet. Computations are performed for the air curtain Reynolds number vanying from 100.5 to 717.8 and the injection slot width ranging from 0.016 to 0.024 m for the air discharge-to-return grille separation distance fixed at 0.2 m and for the cabinet depth of 0.1 m. The temperature difference between the air discharge and ambient is 20 ℃, corresponding to Tj = 5 ℃ and Tamb = 25 ℃. The relative humidities at the air discharge and ambient are respectively fixed at 90% and 60%. Effects of various parameters on the flow, thermal and solutal characteristics in the cabinet are examined in detail. Furthermore, we proceed to investigate the possibility of retarding the air curtain bending by inclining the jet at the air discharge grille toward the ambient. Moreover, how the installation of a secondary air curtain affects the flow in the display cabinet is examined. For the limiting case in the absence of the thermal and solutal buoyancy forces, the results indicate that a single large recirculating vortex is induced by the inertia force of the air curtain for all Reb. However, when the Richardson numbers (buoyancy to inertia ratio) increases to certain level, the air curtain bends toward the cavity and the intrusion of the warm and humid air from the ambient into the cavity becomes relatively prominent. At the same Grt, when the Reb is lowered to some degree, the air curtain bending is so large and two counter-rotating flow recirculations are induced in the cabinet. However, at the same Reb, milder air curtain bending and warm air intrusion are noted at reducing the injection width. Besides, inclining the jet toward the ambient can significantly delay the air curtain bending and the distortions in the isotherms and iso-concentration lines. The results from installing a secondary air curtain indicate that at this low V2j the effects of the jet width and location on the flow are rather slight. But at higher V2j, installing the jet some distance away from the cabinet causes a significant bending of the original air curtain. However, installing a high speed secondary air curtain near the cabinet can substantially reduce the bending of the original air curtain and hence improves the cabinet performance.
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